GB Ordnance Survey: http://www.ordnancesurvey.co.uk/

EDINA — Repository of UK Digital Mapping data and related resources (academic access): http://www.edina.ac.uk/maps/ and http://www.gogeo.ac.uk/ (the EDINA Geoportal)

King’s College London Geodata portal:
http://www.kcl.ac.uk/schools/sspp/geography/research/emm/geodata

MAGIC — Repository of UK Environmental and related data: http://www.magic.gov.uk/

UK Geospatial information Gateway (Data and Standards documents): http://www.gigateway.org.uk/

US Census Bureau: http://www.census.gov/geo/www/index.html

US Geological Survey: http://www.usgs.gov/

US National Spatial Data Infrastructure: http://www.fgdc.gov/nsdi/nsdi.html

US one-stop geoportal: http://gos2.geodata.gov/wps/portal/gos

ESRI Managed Geography Network: http://www.geographynetwork.com/

Geo-community portal: http://www.geocomm.com/

Veryspatial: http://veryspatial.com (GIS podcasts, links and more)